How to simulate a dented surface for metal
First of all you should mime the glossiness of the two helmets. By examining the spreading of light near the highlites you can notice how the object on the right has sharper reflections.



Build a simple material based on a glossy shader with low roughness lit by a nice HDRI iage.



In order to get make the object less smooth we should deform its surfaces. This can be done "physically" by sculpting ridge and vallys or "faked" by altering the normal vector of the faces for example by plugging a noise texture with appropriate scale in a bump node and then in the normal socket of the shader (or wih the displace method as you already introduced).



Each face reflects light toward the camera based on its orientation. If you bend the face's normals, they will start to reflect light the way it would look if the surface was truly deformed. By examining the edges, a viewerwill probably be able to discover the trick, but at a first glance should look good enough amd will help to kee your polycount low.



A second thing to notice is that the object on the right has some little scratches that yours is missing. One of the possible way to reproduce a similar effect could be to use a texture to drive the roughness of the smooth shader.

You could have used the displace/normal method also in this case: they are some kind of surface deformations too, but as the effects has a very small scale I find taking advantage of roughness variation more appropriate.



Final step is to balance the two effect in order to get the wanted result.